Preparation And Properties Of High Performance Polybutadiene-based Polyurethane Underwater Acoustically Transparent Material

In order to ensure hydrophones and sonars can both accurately receive sound signals and not be damaged by seawater,it is of great significance to coat the hydrophones with acoustically transparent cladding layer.Polybutadiene-based polyurethane possesses advantages such as superior acoustic impedance matching with seawater,excellent adhesion property and good low temperature resistance,which is an excellent acoustically transparent encapsulant.This work used polybutadiene-based polyurethane as the matrix material and enhanced its hydrophobicity and mechanical performance by varying the kind and amount of soft and hard segments,which is critical for the advancement of deep seawater acoustic engineering.Polybutadiene-based polyurethane was successfully prepared by toluene diisocynate（TDI）,hydroxyl-terminated polybutadiene（HTPB）,Alcohol-containing chain extenders A and Amine-containing chain extenders B.The results showed that when the NCO content of prepolymer was 9%,the mixing ratio of chain extender was A:B=1:1 and the chain-extension coefficient was 0.95,polyurethane showed a moderate microphase separation and the comprehensive performance of polyurethane achieved the best.The acoustic impedance of polybutadiene-based polyurethane was 1.593×10⁵ g/cm²?s.The volume resistivity and surface resistivity of polyurethane were 3.01×10¹⁵Ω·cm and 1.38×10¹⁵Ω·cm,respectively.Polybutadiene-based polyurethane showed excellent acoustic transparency and electrical insulation property,which could fully meet the basic requirements of underwater acoustically transparent materials.In order to further improve the hydrophobicity,polyurethane was modified by a,ω-dihydroxypoly[（3,3,3-trifluoropropyl）methylsiloxane]（PTFPMS）and 1H,1H,2H,2H-perfluorodecyl trimethoxysilane（FAS-17）.The results showed that the acoustic impedance of FPU-5 at 10 wt%of PTFPMS decreased to 1.584×10⁵ g/cm²?s,which matched better with that of seawater.Meanwhile,due to the introduction of fluoroalkyl groups with low surface energy,the water contact angle of FPU-5 increased to 100°and the water absorption decreased to 0.261%,indicating better hydrophobicity.The water contact angle of FFPU-2 at 4 wt.%of FAS-17increased to 106°while the water absorption decreased to 0.189%.In addition,FAS-17 increased the chemical crosslinking of the system and improved the mechanical property of FFPUs.Fluorosiloxane modified polybutadiene-based polyurethanes exhibited excellent hydrophobicity,acoustic transparency and mechanical properties,which were ideal underwater acoustically transparent materials.Epoxidized hydroxyl-terminated polybutadiene（EHTPB）with excellent hydrophobicity and electrical insulation performance was selected as reinforcing material to prepare epoxy resin modified polybutadiene-based polyurethane.The crosslinking density of polyurethane system increased with the introduction of EHTPB.The results showed that the tensile strength of EPU-5 at 50 wt%of EHTPB was 14.75 MPa and the Shore A hardness was 96.The mechanical strength of EPU exhibited a great improvement comparing with pure polyurethane.The comprehensive analysis showed that EHTPB modified polyurethane had good mechanical strength,hydrophobicity and acoustic transparency,which was expected to be used as the cladding layer in hydrophone and sonar system.There are 41 figures,20 tables and 93 references in this article.